Impact of cigarette versus electronic cigarette aerosol conditioned media on aortic endothelial cells in a microfluidic cardiovascular model

Atherosclerosis is a complex process involving progressive pathological events, including monocyte adhesion to the luminal endothelial surface. We have developed a functional in vitro adhesion assay using BioFlux microfluidic technology to investigate THP-1 (human acute monocytic leukaemia cell) monocyte adhesion to human aortic endothelial cells (HAECs). The effect of whole smoke conditioned media (WSCM) generated from University of Kentucky reference cigarette 3R4F, electronic cigarette vapour conditioned media (eVCM) from an electronic nicotine delivery system (ENDS) product (Vype ePen) and nicotine on monocyte adhesion to HAECs was evaluated. Endothelial monolayers were grown in microfluidic channels and exposed to 0–1500 ng/mL nicotine or nicotine equivalence of WSCM or eVCM for 24 h. Activated THP-1 cells were perfused through the channels and a perfusion, adhesion period and wash cycle performed four times with increasing adhesion period lengths (10, 20, 30 and 40 min). THP-1 cell adhesion was quantified by counting adherent cells. WSCM induced dose-dependent increases in monocyte adhesion compared to vehicle control. No such increases were observed for eVCM or nicotine. Adhesion regulation was linked to increased ICAM-1 protein expression. Staining of ICAM-1 in HAECs and CD11b (MAC-1) in THP-1 cells demonstrated adhesion molecule co-localisation in BioFlux plates. The ICAM-1 adhesion response to WSCM was downregulated by transfecting HAECs with ICAM-1 siRNA. We conclude that the BioFlux system is able to model human monocyte adhesion to primary human endothelial cells in vitro and WSCM drives the greatest increase in monocyte adhesion via a mechanism involving endothelial ICAM-1 expression.